1. Field of the Invention
This invention relates generally to micromechanical and related modulation of optical circuits and networks; and more particularly to methods and apparatus for providing faster switching or modulation with lower power than heretofore required for imaging.
2. Related Art
A seminal effort in this field is U.S. Pat. No. 4,988,157 of Jackel—assigned to Bell Communication. That patent teaches use of a chemically (to be more specific, electrolytically) creatable and destroyable bubble, and its implications on total internal reflection, for optical modulation.
U.S. Pat. Nos. 5,699,462 and 5,960,131 of Fouquet et al., and U.S. Pat. No. 5,978,527 of Donald, represent applications of the thermal-inkjet technology refinements of Hewlett Packard Company to light modulation or switching. Though faster than electrolysis, thermal effects operate on the order of milliseconds and accordingly are far from optimal in switching speed.
U.S. Pat. No. 5,619,600 of Pohl and U.S. Pat. No. 5,774,252 of Lin et al. represent entries in somewhat related fields on behalf of IBM and Texas Instruments, respectively; and Japanese publication 5-49055 of 1993 teaches a related effort by Nippon Telegraph & Telephone Corporation. Pohl teaches tunneling of light through liquid metal, for pathlengths on the order of a fractional wavelength; while possibly useful for kilohertz CW modulation, this technique too is relatively slow for switching.
Many or most lidar and related imaging systems are bulky and heavy, and require relatively high operating power—leading to operational inconvenience and expense. Curiously enough, one reason for these undesirable characteristics is the bulk and weight associated with apertures used in transmitting and then receiving optical signals.
Although philosophically speaking an aperture is in essence no more than a hole, in actual practice the hardware (including lenses and the like when present) typically associated with an aperture is bulky and heavy. Heretofore it has not been taught how to mitigate this problem in the lidar field.
A related persistent problem in known lidar systems is maintenance of good signal separation as between different parts of an object region of interest. The Bowker patent mentioned above, for example, projects a fan-shaped pulse beam to a wide-cross-track region of the ocean surface (and interior)—and receives reflection back from the entire region.
To the extent that some element of the beam is reflected laterally within the turbid ocean volume and returns from a different point than its impingement point, this system is subject to crosstalk. The patented teachings offer no correction for this phenomenon.
Other drawbacks commonly encountered are issues concerning field of view, speed and maneuverability of the system. Many of these systems are limited to a relatively small field of view and so require the use of multiple complete systems or repeated imaging from several positions.
The field of regard for many conventional optical systems is increased by an external scan mirror that allows the system to address a field that is larger than their field of view. This is done by rotating the external mirror relative to the optics (FIG. 10). Equivalently the entire optical system is sometimes mounted within a gimbal to rotate the entire optical system (FIG. 11).
Other systems, analogously, are further limited by the visual field that can be surveyed at any one instant in time because of components that must operate in sequence rather than independently. These drawbacks increase the importance of having a compact, maneuverable system capable of high-speed imaging that doesn't require multiple setups.
In addressing these shortcomings, it is also important to use alternatives that are based on broadly established and available parts and technologies. Economical concerns favor the use of such parts, especially if they can be reproduced in high volumes and offer the possibility of inexpensive rapid start-up of commercial exploitation.
While some conventional systems may address some of these shortcomings individually, what is needed is a versatile system that is both maneuverable, economical, and capable of being adapted to a wide variety of applications involving detecting, ranging and imaging in different environments. This adaptability should not be limited to use in different applications, but should also allow the flexibility to choose instrumentation and light sources depending on one's needs and preferences for a given project.
Another economic factor of concern includes power requirements for driving any attached light sources. Still another is the circuitry necessary to satisfy these power requirements.
As can now be seen, the related art remains subject to significant problems. The efforts outlined above—although praise-worthy—leave room for considerable refinement.